Since organic electroluminescence devices are capable of obtaining a light emission with high luminance intensity by driving at a low voltage, the devices have been actively researched and developed recently. Generally, organic electroluminescence devices have an organic layer including a light emitting layer interposed between a pair of electrodes, and utilize, for light emission, energy of the exciton generated as a result of recombination of electrons injected from a cathode and holes injected from an anode in the organic layer.
Improvement in the efficiency of devices has been recently made by using a phosphorescence emitting material. As a phosphorescence emitting material, iridium complexes, platinum complexes and the like are known (for example, see Patent document 1). Further, among them, Ir(btp)2(acac) is known as a red phosphorescent material.
In addition, a doping type device using a light emitting layer in which a light emitting material is doped into a host material has been widely adopted. Host material is actively developed, and as a host material for red phosphorescent device, examples of using CBP(4,4′-bis(N-carbazolyl)biphenyl) and Balq(Aluminum(III)bis(2-methyl-8-quinolinato)-4-phenylphenolate) have been well known (for example, see Patent document 2).
For example, Patent document 2 discloses an invention in which an aromatic polycyclic condensed ring-based material is used in a host material of a red phosphorescent material in order to manufacture a device having high efficiency and a long life-span. However, luminous efficiency of the device, and durability when driving at a high temperature of the device are not sufficient. Moreover, when considering a use for display or illumination, there is a problem in that chromaticity is changed according to driving, and thus, an improvement is required.
Conventionally, in the evaluations of the durability of the device, a change in chromaticity according to driving has been used as an evaluation item of the properties of organic electroluminescence devices along with increase in driving voltage or decrease in efficiency. Further, the evaluation of the environmental temperature from room temperature to a high temperature (mainly as a meaning of an acceleration test) has also been conducted. However, it has been unnoticed that variation in chromaticity increases when driving at a high temperature as compared with when driving at a lower temperature, and when considering the use of a in-vehicle panel which may be maintained at a high temperature of 80° C. or more, it may be expected that the change in chromaticity when driving at a high temperature becomes a serious problem.